I haven't been able to track down who first tweeted this, mostly because it's spread so far and wide that Twitter search can't get far enough back in time to find Tweet 0. I think it might be @vvondra, Vojtěch Vondra, who Tweeted it on the 10th, but I wouldn't be surprised if it's a much older joke than that. (If you know, fill me in, and I'll give proper attribution.)

Update: @cun is a contender, according to Chris Combs in the comments, having sent the joke out on January 10th as well. Several people on Twitter pointed out this variation, too, which appears to antedate the bar joke:

How many SEO copywriters does it take to change a lightbulb, light bulb, light, bulb, lamp, bulbs, flowers, flour...?